1. Field of the Disclosure
The present disclosure relates generally to a wireless communication system, and more particularly, to an apparatus and a method for feeding back channel information in a wireless communication system.
2. Description of the Related Art
To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Institute of Electrical and Electronics Engineers (IEEE) 802.11ax standard, which is the next generation wireless local are network (LAN) standard, aims to improve the performance experienced by a user in an environment that is dense with LAN access points (APs) and users (or stations (STAs)). In such a dense area, dozens of stations may be allocated to a single AP, and communication limitations are attributed since only the multiple user-multiple input multiple output (MU-MIMO) scheme that is supported by the existing wireless LAN standard IEEE 802.11ac is used.
Through the MU-MIMO scheme of the IEEE 802.11ac standard, it is possible to simultaneously transmit signals to up to four stations. In order to transmit signals to four STAs at the same time, a transmitting station requires the channel information on the four stations, and the channel information is required to be fed back from each station. The IEEE 802.11ac standard supports a technique in which up to four STAs feed back their own channel information. In the IEEE 802.11ac standard, the STAs that can simultaneously transmit signals are limited to four STAs, and in order to increase the number of simultaneously-transmittable STAs, the number of antennas must be increased. The number of antennas that can be installed in a transmitter is limited by the physical space. In addition, although the number of antennas increases, the time required for the feedback increases as the number of STAs increases, when using the 802.11ac-based method. This lowers the transmission efficiency in the concentrated area causing congestion.
Although the IEEE 802.11ac standard does not support the orthogonal frequency division multiple access (OFDMA) technique, it is expected that the IEEE 802.11ax will adopt the OFDMA technique. The OFDMA technique allocates subcarriers to different users, thereby enabling a multi-connection so that various effects, such as, for example, an increase in system capacity, can be obtained. By supporting the OFDMA technique, additional resources can be minimized and the number of concurrent users can be increased, thereby improving the performance a user experiences in a dense environment.